Biology subjects

Juhasz, G.

Publications and source records attributed to Juhasz, G..

10 recordsLinked to original sources

bioRxiv2026

The Uvrag-containing PI3K complex promotes Hsc70-4 dependent endosomal clathrin removal and lysosomal maturation in Drosophila nephrocytes

The class III phosphatidylinositol 3-kinase complex (PI3K(III)) generates phosphatidylinositol-3-phosphate (PI(3)P), a lipid that defines endosomal membrane identity. Two PI3K(III) complexes share core subunits but differ in their fourth component: the Atg14-containing complex I functions in autophagy, whereas the Uvrag-containing complex II is required for endosomal maturation. Despite this, the mechanism by which complex II promotes lysosomal function remains unclear. Using Drosophila nephrocytes, we show that PI(3)P is enriched on Rab7-positive late endosomes and that the Hsp70 chaperone Hsc70-4 binds phosphoinositides. Loss of PI3K complex II disrupts endolysosomal organization and phenocopies Hsc70-4 inhibition. In both cases, clathrin accumulates on intracellular, often endosomal membranes, Rab7 compartments are disorganized, and abnormal endolysosomal structures form. These defects are accompanied by impaired HOPS recruitment, lysosomal dysfunction, and secretion of endolysosomal content. Importantly, clathrin depletion partially rescues these defects. Together, our findings identify a role for PI3K complex II in promoting clathrin removal from endosomal membranes and link PI(3)P and Hsc70-4 activity to lysosomal maturation.

cell biology↗

bioRxiv2026

Multiple overlapping SNARE complexes drive endosome maturation in Drosophila nephrocytes

Endosomal maturation determines whether internalized cargo is recycled or degraded, yet the molecular logic governing early endosomal fusion remains poorly defined. This process is often depicted as a linear Rab5-to-Rab7 transition mediated by a single, ordered SNARE pathway, but extensive redundancy in mammalian systems has obscured pathway architecture. Here, using Drosophila nephrocytes as a genetically tractable in vivo model with minimal SNARE redundancy, we show that early endosome maturation is driven by multiple parallel, non-interchangeable SNARE-dependent pathways. We first resolve a long-standing discrepancy in Syntaxin 7 family orthology, demonstrating that the Drosophila protein previously termed Syx7/Avl is functionally analogous to mammalian STX12 rather than STX7, while late endosomal and lysosomal fusion is mediated by a distinct Syntaxin 7 homolog (Syx13). Based on this reclassification, we define a Syx12L-Snap29-Ykt6 complex that drives canonical homotypic early endosomal fusion. In addition, we identify two related SNARE assemblies - Syx7L-Snap29-Ykt6 and Syx7L-Snap29-Vamp7-that promote later stages of endosomal and lysosomal fusion with distinct Rab GTPase requirements. These partially compensatory complexes remain active when the canonical pathway is disrupted, producing divergent morphological outcomes, including the formation of aberrant endolysosomal swirls. We establish Snap29 as a central Qbc-SNARE integrating all endosomal fusion routes and uncover a dual role for Ykt6 in promoting maturation while also participating in endosomal recycling. Together, our findings revise the prevailing model of endosome maturation, revealing a network of parallel, regulated fusion pathways that confer robustness and plasticity to the endolysosomal system.

cell biology↗

bioRxiv2025

Ubiquitination of secretory granules promotes crinophagic degradation in Drosophila

Gland cells dynamically regulate their secretory granule content via balancing the rates of synthesis, maturation, secretion, and lysosomal degradation (crinophagy). The signal(s) leading to crinophagic breakdown of secretory granules are unknown. Here we show that dynamic ubiquitination of unreleased or low-grade glue-containing secretory granules marks these vesicles for crinophagy in larval salivary gland cells of Drosophila. We identify the ubiquitin ligase Cnot4 and the deubiquitinating enzyme Usp7 as mediators of glue granule ubiquitination and deubiquitination, respectively. Loss of either Cnot4 or Usp7 impairs glue granule fusion with lysosomes. Overexpression of Cnot4 induces premature crinophagy while Usp7 overexpression prevents developmental crinophagy via modulation of glue granule ubiquitination status. Our work establishes that ubiquitination of secretory granules is a key trigger of crinophagy in Drosophila, paving the way for further analysis of this barely characterized degradation route in Metazoans.

cell biology↗

bioRxiv2025

Huntington's disease-associated ankyrin repeat palmitoyl transferases are rate-limiting factors in lysosome formation and fusion

Protein palmitoylation in the Golgi apparatus is critical for the appropriate sorting of various proteins belonging to secretory and lysosomal systems, and defective palmitoylation can lead to the onset of severe pathologies. HIP14 and HIP14L ankyrin repeat-containing palmitoyl transferases were linked to the pathogenesis of Huntingtons disease, however, how perturbation of these Golgi resident enzymes contributes to neurological disorders is yet to be understood. In this study, we investigated the function of Hip14 and Patsas - the Drosophila orthologs of HIP14 and HIP14L respectively - to uncover their role in secretory and lysosomal membrane trafficking. Using larval salivary gland, a well-established model of the regulated secretory pathway, we found that these PAT enzymes equally contribute to the proper maturation and crinophagic degradation of glue secretory granules by mediating their fusion with the endo-lysosomal compartment. We also revealed that Patsas and Hip14 are both required for lysosomal acidification and biosynthetic transport of various lysosomal hydrolases, and we demonstrated that the rate of secretory granule-lysosome fusion and subsequent acidification positively correlates with the level of Hip14. Furthermore, Hip14 is also essential for proper lysosome formation and neuronal function in adult brains. Finally, we found that the over-activation of lysosomal biosynthetic transport and lysosomal fusions by the expression of the constitutively active form of Rab2 could compensate for the lysosomal dysfunction caused by the loss of Patsas or Hip14 both in larval salivary glands and neurons. Therefore, we demonstrated that ankyrin repeat palmitoyl transferases may act as rate-limiting factors in lysosomal fusions and provide genetic evidence that defective protein palmitoylation and the subsequent lysosomal dysfunction can contribute to the onset of Huntingtons disease-like symptoms. Author SummaryGrowing body of evidence suggests that decreased activity of HIP14 and HIP14L palmitoyl transferases caused by accumulation of mutant Huntingtin and the subsequent alterations in protein palmitoylation play a critical role in the onset of Huntingtons disease (HD). However, which cellular processes are perturbed and eventually lead to the emergence of HD due to impaired palmitoylation is still poorly understood. In our study, we used a Drosophila model to uncover the role of Hip14 and Patsas (the fly ortholog of HIP14L) in secretory and lysosomal membrane trafficking. We found that silencing of these transferases in larval salivary glands equally disrupts secretory granule lysosome-fusion, their subsequent acidification and also the trafficking of lysosomal hydrolases. While overexpression of Hip14 resulted in the acceleration of these processes. We also observed that neuron-specific loss of Hip14 not only perturbs lysosome formation but also results in a progressive decline in neuromuscular functions. Importantly, both lysosomal and neuronal defects emerging in Hip14 and Patsas deficient backgrounds could be restored by hyperactivation of Rab2 GTPase mediated lysosome formation and fusion. These findings suggest that Hip14 and Patsas protect from the onset of HD like symptoms by acting as rate-limiting factors of lysosome formation and fusion.

cell biology↗

bioRxiv2024

Selective autophagy fine-tunes Stat92E activity by degrading Su(var)2-10/PIAS during glial injury signalling in Drosophila

Glial immunity plays a pivotal role in the maintenance of nervous system homeostasis and in responses to stress conditions, including neural injuries. The transcription factor Stat92E is activated independently of the canonical JAK/STAT pathway in Drosophila glial cells following central nervous system injury to shape glial reactivity towards degenerating axons. However, the upstream regulatory mechanisms governing Stat92E activation remain elusive. Here we reveal that selective autophagy mediates degradation of the PIAS SUMO ligase family member Stat92E repressor, Su(var)2-10 in glia. Autophagic elimination of Su(var)2-10 mediated by its co-localization and interaction with the core autophagy factor Atg8a is required for efficient Stat92E-dependent transcription after injury. In line with this, we demonstrate that autophagy is essential for the upregulation of an innate immune pathway in glial cells following axon injury, characterized by the induction of virus-induced RNA 1 (vir-1). We propose that autophagic Su(var)2-10 breakdown controls Stat92E activation to allow glial reactivity. These findings identify a critical role for autophagy in glial immunity as part of neural injury responses.

neuroscience↗

bioRxiv2024

The Rab7-Epg5 and Rab39-ema modules cooperately position autophagosomes for efficient lysosomal fusions

Macroautophagy, a major self-degradation pathway in eukaryotic cells, utilizes autophagosomes to transport self-material to lysosomes for degradation. While microtubular transport is crucial for the proper function of autophagy, the exact roles of factors responsible for positioning autophagosomes remain incompletely understood. In this study, we performed a loss-of-function genetic screen targeting genes potentially involved in microtubular motility. A genetic background that blocks autophagosome-lysosome fusions was used to accurately analyze autophagosome positioning. We discovered that pre-fusion autophagosomes move towards the non-centrosomal microtubule organizing center (ncMTOC) in Drosophila fat cells, which requires a dynein-dynactin complex. This process is regulated by the small GTPases Rab7 and Rab39 together with their adaptors: Epg5 and ema, respectively. The dynein-dependent movement of vesicles toward the nucleus/ncMTOC is essential for efficient autophagosomal fusions with lysosomes and subsequent degradation. Remarkably, altering the balance of kinesin and dynein motors changes the direction of autophagosome movement, indicating a competitive relationship where normally dynein-mediated transport prevails. Since pre-fusion lysosomes were positioned similarly to autophagosomes, it indicates that pre-fusion autophagosomes and lysosomes converge at the ncMTOC, which increases the efficiency of vesicle fusions.

cell biology↗

bioRxiv2024

Neuronal phenotype defined by transcriptome-wide bursting kinetics in pyramidal and fast-spiking cells

Single-cell sequencing revealed the transcriptional heterogeneity of neurons and introduced transcriptome-defined neuron types and subtypes. Temporal recordings of gene transcription showed that mRNA synthesis is arranged into transcriptional bursts which can be characterized by kinetic parameters. Here, we selected two distinct, functionally homogenous, and electrophysiologically well-defined neuronal cell types - the pyramidal cells and fast-spiking interneurons - for transcriptional burst analysis. Hierarchical clustering based on electrophysiological parameters recovered these cell types. In contrast, clustering based on transcripts failed to differentiate these neuronal phenotypes. We applied mathematical models to analyze burst kinetics of fast-spiking and pyramidal cells to explore the transcriptional underpinning of their distinct physiological functions. We found that inferred burst kinetic parameters are distinct measures of gene expression from average mRNA counts. Based on our results, we suggest that burst kinetics can be considered as a component of transcriptome-defined neuronal phenotype besides mRNA counts.

bioinformatics↗

bioRxiv2023

Complex-specific subunits of endosomal tethering factors determine the balance between HOPS/CORVET complexes

The endolysosomal tethering complexes HOPS and CORVET play pivotal roles in the homo- and heterotypic fusion of early and late endosomes, respectively, and HOPS also mediates the fusion of lysosomes with incoming vesicles including late endosomes and autophagosomes. These heterohexameric complexes share their four core subunits that assemble with additional two, complex-specific subunits. These features and the similar structure of the complexes allow the formation of hybrid complexes, and the complex specific subunits may compete for binding to the core. In our study, we decided to gain insight into how human HOPS and CORVET complexes form. We found that the overexpression of CORVET-specific Vps8 or Tgfbrap1 decreased the amount of core proteins Vps11 and Vps18 that are assembled with HOPS-specific subunits Vps41 or Vps39, which suggests reduced amount of intracellular HOPS. In line with this, we observed that the level of lipidated LC3 protein was elevated in these cells and the autophagic cargo p62 showed accumulation in cells overexpressing Vps8, suggesting failure in autophagosome-lysosome fusion in line with loss of HOPS function. In contrast, overexpression of HOPS-specific Vps39 or Vps41 did not affect the levels of these autophagic markers. Finally, we found that a hybrid complex containing Vps39 and Vps8 could be formed in HEK293 cells.

cell biology↗

bioRxiv2020

Vps13D is required for mitochondrial fission and mitophagy triggered by fission defects in Drosophila neurons

A healthy population of mitochondria, maintained by proper fission, fusion, and degradation, is critical for the long-term survival and function of neurons. Here, our discovery of mitophagy intermediates in fission-impaired Drosophila neurons brings new perspective into the relationship between mitochondrial fission and mitophagy. Neurons lacking either the ataxia disease gene Vps13D or the dynamin related protein Drp1 contain enlarged mitochondria that are engaged with autophagy machinery and also lack matrix components due to rupture. Reporter assays combined with genetic studies imply that mitophagy both initiates and is completed in Drp1 impaired neurons, but fails to complete in Vps13D impaired neurons, which accumulate compromised mitochondria within stalled mito-phagophores. Our findings imply that in fission-defective neurons, mitophagy becomes induced, and that the lipid channel containing protein Vps13D has separable functions in mitochondrial fission and phagophore elongation.

cell biology↗

bioRxiv2020

Educational attainment polygenic scores in Hungary: evidence for validity and a historical gene-environment interaction

Educational attainment is a substantially heritable trait, and it has recently been linked to specific genetic variants by genome-wide association studies (GWASs). However, the effects of such genetic variants are expected to vary across environments, including countries and historical eras. We used polygenic scores (PGSs) to assess molecular genetic effects on educational attainment in Hungary, a country in the Central Eastern European region where behavioral genetic studies are in general scarce and molecular genetic studies of educational attainment have not been previously published. We found that the PGS is significantly associated with highest educational level attained as well as the number of years in education in a sample of Hungarian volunteers (N=829). In an English (N=976) comparison sample with identical measurement protocols the same PGS had a stronger association with educational level, but not with years in education. In line with previous Estonian findings, we found higher PGS effect sizes in Hungarian, but not in English participants who attended higher education after the fall of Communism, although we lacked statistical power for this effect to reach significance. Our results provide evidence that polygenic scores for educational attainment are valid in diverse European populations.

genetics↗